FoxBridge

© 2026 Jennifer K. Mellen

FoxBridge lets Claude Code drive Firefox the way Claude in Chrome drives Chrome.

Parts

• extension/ - Firefox extension (Manifest V2, persistent background). Connects to ws://127.0.0.1:47821.

• server/index.js - MCP server (stdio) plus the local WebSocket bridge. No dependencies; needs Node 18+.

• .claude-plugin/, .mcp.json, skills/ - Claude Code plugin packaging. The repo is its own plugin marketplace.

Related MCP server: Kamurafox

Install

Needs Node.js 18 or newer and Claude Code.

1. Claude Code plugin - in Claude Code run:

   /plugin marketplace add mellenfamilymail-lgtm/foxbridge
   /plugin install foxbridge@foxbridge

2. Firefox add-on - install it from addons.mozilla.org/firefox/addon/foxbridge-for-claude (works in any Firefox once Mozilla's review is done). Until then:

   • Use Firefox Developer Edition, open about:config and set xpinstall.signatures.required to false.

   • Download foxbridge.xpi from Releases and drag it into Firefox.

3. Restart Claude Code and ask it to do something in Firefox.

Claude Desktop (Chat App)

FoxBridge also works in the Claude desktop app, not just Claude Code:

1. Download foxbridge.mcpb from Releases.

2. Double-click it (or drag it into Claude Desktop under Settings > Extensions) and click Install.

3. Install the Firefox add-on as in step 2 above, then ask Claude to "list my Firefox tabs".

Unsigned Builds

FoxBridge is not listed in Anthropic's plugin directory (local MCP servers are accepted there only from Verified organizations), and the Firefox add-on is unsigned until Mozilla's review is done. You can still use every part:

• Claude Code plugin - install it from this repo with the /plugin commands above. The directory listing is not needed.

• Claude Desktop - foxbridge.mcpb is unsigned. Claude Desktop shows an "unverified" warning; click Install to continue.

• Firefox add-on - in Firefox Developer Edition or Nightly, set xpinstall.signatures.required to false in about:config, then drag foxbridge.xpi into Firefox. In regular Firefox, open about:debugging > This Firefox > Load Temporary Add-on and pick foxbridge.xpi; it is removed when Firefox restarts.

Unsigned builds are used at your own risk. They come from this repository only; do not install copies from anywhere else.

Check It Works

In Claude Code, ask: "List my Firefox tabs." Claude should answer with your open tabs. The FoxBridge toolbar icon in Firefox shows an "off" badge while Claude is not connected, and no badge once it is.

How to Use

Keep Firefox open, then ask Claude in plain words. You don't need to name the tools. Some examples:

• "List my Firefox tabs."

• "Open https://example.com in Firefox and tell me what the page says."

• "Search Firefox for 'weather Boston' and read me the forecast."

• "Fill in the contact form on this page with my name and email, but don't submit it."

• "Take a screenshot of the current Firefox tab."

• "Open my web app at http://localhost:3000, click Sign Up and tell me about any console errors."

• "Check the network requests on this page for failed calls."

Tips:

• Claude works in your real Firefox, so it can see sites you are already signed in to. Stay at the computer when it is filling in forms or clicking buttons.

• Tell Claude to ask before it submits, sends, buys or deletes anything.

• Only one Claude session can drive Firefox at a time.

• Firefox doesn't let any add-on work on about: pages or addons.mozilla.org.

Troubleshooting

• "Firefox is not connected" - make sure Firefox is open with FoxBridge enabled (about:addons), then wait a few seconds; it reconnects every 2 seconds.

• Badge stays "off" - restart Claude Code. Only one Claude Code session can drive Firefox at a time; close the other one.

• Port 47821 is in use - set the FOXBRIDGE_PORT environment variable to another port before starting Claude Code.

• Add-on "could not be verified" - you are on regular Firefox. Use Developer Edition with xpinstall.signatures.required set to false until the signed version is on addons.mozilla.org.

• Tools not listed in Claude Code - run /plugin and check that foxbridge is enabled, and that node --version shows 18 or newer.

• Nothing happens on some pages - Firefox blocks all extensions on about: pages and addons.mozilla.org.

Uninstall

Run /plugin uninstall foxbridge@foxbridge in Claude Code and remove FoxBridge from about:addons in Firefox.

Build from source

npm run build writes dist/foxbridge.xpi. npm run build:mcpb writes the Claude Desktop extension dist/foxbridge.mcpb. node test/smoke.js runs a live test against an open Firefox.

Tools

tabs_list, tabs_create, tabs_close, tabs_select, navigate, screenshot, read_page, find, get_page_text, click, type, key, scroll, form_input, javascript, console_messages, network_requests, wait.

Known limits

Input events are synthetic (isTrusted = false). A planned WebDriver BiDi mode will add trusted input.